He (the next door neighbour) has threatened me with a knife before, his Dad
died in a mental instituition (a little research found that out) and today
he spent 20 minutes walking around his back garden while talking to himself
and saying he will kill That Dick (his nickname for me) and That Fat *******
(his nickname for his other next door neighbour).

Wonder if you can get him sectioned under the mental health act ? -
certainly sounds like he needs assessment...